Process for dehydrogenation of olefins



United States Patent U.S. Cl. 260-680 Claims ABSTRACT OF THE DISCLOSUREA catalytic process for the oxidative dehydrogenation of mono-olefins tothe corresponding diolefins employing a catalyst of mixed oxides ofmolybdenum, bismuth and cerium. The mono-olefin passes through areaction zone containing the catalyst, at temperatures from 350 to 650C., usually at about atmospheric pressure.

BACKGROUND OF THE INVENTION This invention relates to a process for theproduction of conjugated diolefins. More particularly, it relates to thecatalytic preparation of conjugated diolefins from mono-olefins byoxidative dehydrogenation.

It is known to employ oxidative dehydrogenation to produce conjugateddiolefins from the corresponding mono-olefins.

U.S. Patent No. 2,991,320 discloses the use of mixed oxides of bismuthand molybdenum to catalyze the oxidative dehydrogenation of olefins tothe corresponding diolefins. British Patent No. 965,200 disclosespromoter catalysts of boron, manganese, or phosphorus oxides to improvethe performance of the primary catalyst. The'se catalysts, often dilutedwith inert materials, are placed in contact with the mono-olefin feedstream at optimum temperature and pressure conditions. The eflluent iscollected, and the desired product is separated from unreacted feedmaterials, reaction by-products, and any inert diluent which may 'bepresent. The physical size and shape of the catalyst may vary, dependingon the type of reaction chamber employed. Fluidized-bed reactors use acatalyst in powder form, while fixed-bed reactors use larger pellets orgranules.

Catalysts of this type are prepared by combining salts of the desiredmetals in proportions so that their oxides will have the desiredcomposition. The salts are precipitated with an inert material (usuallysilica or alumina) dried, and fired to produce the desired mixture ofoxides.

In the manufacture of conjugated diolefins by these known processes,stress is placed on achieving both a high degree of conversion of thefeed material and a high selectivity. Conversion is defined as thatpercentage of the incoming feed material which is chemically changed inthe reaction zone. Obviously, this figure may be obtained by subtractingfrom 100% that percentage of the feed material which passes through thereaction zone unchanged or, in the case of an olefin, is isomerized only'ice to the extent of shifting the position of the carbon-carbon doublebond without changing the carbon skeleton and is recovered along withthe reaction products and whatever inert material was used as a diluent.Selectivity is here defined as the mole percentage of desired diolefinformed based on the moles of mono-olefin reacted. Other considerationsmay also be important, such as, for instance, catalyst life, ease ofregeneration, and numerous other conditions. The value and efliciency ofthe process, however, may be determined by the values of conversion andselectivity. Thus, a means of improving these two values is of primeimportance to the manufacturer.

SUMMARY OF THE INVENTION It is therefore an object of the instantinvention to provide a process for the conversion of mono-olefins to thecorresponding conjugated diolefins by means of an oxidativedehydrogenation reaction with improved conversion and selectivity.

According to this invention, the addition of cerium oxide to the knowncatalyst system of bismuth and molybdenum oxides gives substantialimprovements in both conversion and selectivity in this oxidativedehydrogenation reaction. By including minor amounts of cerium oxide asa promoter catalyst, unexpected increases in th efiiciency of theprocess are obtained. 1

DESCRIPTION OF THE PREFERRED EMBODIMENTS Catalyst The catalyst of theinvention can be produced by combining the oxides of bismuth, molybdenumand cerium in any convenient manner to produce a homogeneous mixture.Conveniently, the component materials can be mixed in water solution,and the water evaporated oif. The mixture can then be fired at anelevated temperature to convert any salts which may be present to thecorresponding oxides. The temperature during the firing operation shouldbe high enough to convert substantially all the salts present intooxides, but should not exceed 600 C., and should preferably stay below550 C. The atomic ratio of bismuth to molybdenum should be at least tenatoms of bismuth to one hundred atoms of molybdenum, and is preferablyfrom about 5 to 18 times this minimum. The atomic ratio of cerium tomolybdenum can vary quite widely from 2.5 or fewer atoms of cerium up to50 or more atoms of cerium per atoms of molybdenum. In general, nobenefit is noticed with the higher levels of cerium, and the amount usedwould probably be kept low, for cost reasons.

The catalyst can be used by itself, in unsupported form, but is usuallycombined with an inert material, such as silica or alumina for ease ofhandling. The amount of inert material used will rarely exceed about 50%by weight of the total. Where pellet form or large granules are desired,the catalyst mixture can be prepared for firing in its desired finishedshape and size. When smaller particle size is required, the firedcatalyst may be ground and sieved to obtain the desired sizedistribution.

Feed material The feed material of the invention is a mono-olefin,

ferred temperature range is from about 400 C. to about 550 C.

Pressure The reaction will proceed at atmospheric pressure, and

or mixtures of mono-olefins, having from four to seven 5 is generallyrun at pressures ranging from one-half to five carbon atoms. Thesematerials include, for example, atmospheres. Higher pressures may beemployed, howbutene-l, cisor trans-butene-Z, pentene-l, cisor transever,if desired, up to twenty atmospheres or more. pentene-2, 3 methylbutene-l, 2 methyl butene-Z, 2- methyl butene-l, hexene-l, cisortrans-hexene-2, and Ractlon rates cyclohexene. The invention is directedprincipally to the Rates of l'eactlon W1 11 be ChaTacter1Zed bY i fefidmanufacture of 1,3-butadiene and isoprene, but may also Tate 0f themono-016131116 hydrocarbon T rate be used in producing the otherconjugated diolefins de- Pressed as the gaseous hourly Space Velocity,abbfsvlated i d f h kii f d to b as GHSV. The GHSV is defined as volumesof reactant gas (calculated at standard conditions, 0 C. and 760 mm.) 15Drluent passed per hour per unit volume of the cataylst bed. GHSV valuesof from 30 to about 1 000 can be used to An 1nert gas can be mcluded asa diluent 1n the process of the to by 222E225;fifivliii ittfiiiliififitiittifif lowering the partial pressure of the desiredproduct in the b1 e pro ems can arlse 1n removmg heat from the reactioneffluent mixture. The presence of a d1luent also acts to zone. Preferredolefin GHSV values for the reactlon of reduce the concentration ofoxygen 1n the mixture below this invention are from about 80] to about350 the minimum required for combustion of the feed hydrocarbons. Suchmaterials as nitrogen, argon, or carbon EXAMPLE 1 dioxide can beemployed for this purpose, although they are not necessary forsuccessful operations. The use of a y P f by first comblllmg thediluents presents a problem in the recovery step, as the lowlngIngredients 111 Solution: separation of these inert materials can bedifficult. Water vapor used as a diluent avoids this difficulty, byoffering an inexpensive diluent which can be readily condensed T estcatalyst out of the effluent stream at convenient temperatures andMaterlal Control (MO-I-Bl) (Mo+B1+Ce) pressures. The amount of watervapor used is not at all 85% M003 (g) 5 9 5 9 critical and can rangefrom none up to about twenty or Bi N03)3.5H26'( 1210 1210 more times thevolume of the feed stock, although a pregig g a {70%) 1 1 ferred levelis from three to ten tunes the volume of the Hz0 dl$tll1ed) (m1.) s smono-olefin feed stock S01 7 Oxygen Oxldatlve dyhydfggenagm gfi Theprecipitates that formed on mixing the above ini O g l g zq gi g ee 40gredients were evaporated to dryness and were then fire: 3. 2 fi i fi. ee onefmo e o wa er g f' for 16 hours at an average temperature of 540 C.The e s 016 lometnc quanmy 0 oxygen requue catalysts were then ground toa particle size of from 10 one-half mole per mole of olefin. Recommendedamounts to 20 mesh i gg s g alljout and i The above combinations arecalculated toyield 0 g moe mygen 5 6 P catalysts having atomic ratios(MozBizCe) of 100:71.5 :0 pre are e oxygep may 6 supp as y for thecontrol and l00:7l.5:2.87 for the test catalyst. pure oxygen, or as arr.The use of air necessanly introduces a significant quantity of inertgas, primarily nitro- EXAMPLE 2 gen, which moreases the problem ofnon-condensable Using the catalysts prepared in Example 1 above, gasesthe effluent-The cost Savmgs m usmg 15 hydrogenation of l-butene wasaccomplished, as follow;- Pensatmg relatlve to the use of Pure oxygen- Amixture of l-butene, air and steam was passed through T t a reactionZone containing the catalysts of Example 1 empera me in a particle sizeof 10 to 20 mesh. Five volumes of air The reaction of the invention willproceed appreciably and from eight to ten volumes of steam were mixedwith at temperatures as low as 350 C., and may be accomeach volume ofhydrocarbon feed. The feed mixture plished at temperatures as high asabout 650 C. or above. passed through a pro-heat section, through thereaction Higher temperatures, as may be expected, give higher zone, andinto the recovery area, where the product conversion rates, butselectivities tend to decrease somecomposition was analyzed by gaschromatography. The what as the reaction temperature increases. Theprefollowing measurements were recorded:

Run

A B o D Catalyst BH-Mo Bi+Mo Bi+Mo+Ce Bi-l-M0+Ce Temp" 0-- 464 479 472430 473 473 464 471 GHSV 109 109 116 116 87 87 123 123 Percentconversion- 79. 0 81. 6 86. 2 84. 2 84. 1 86. 2 91. 3 88. 1 Percentselectivity 80. 8 86.1 79. 3 81. 8 85. 4 84. 7 83. 3 86. 2 Percentbutadiene yield 63.7 70. 2 68.5 68.8 71.8 73. 2 77.1 76. 0 Percent 00 m-8. 5 7.8 13. 0 10.6 10.0 8.8 10.1 8.2 Percent o0 6.5 3.3 4.6 4. a 0.92.7 3. 0 3. 0 Percent coke 0. 25 0. 26 0. 17 0. 93 0. 93 0. 91 0. 91 0.91

5 EXAMPLE 3 In a similar manner, the cerium-containing catalyst ofExample 1 was used in the production of isoprene from different isomersof isoarnylene. Again five volumes of air and from eight to ten volumesof steam per volume of hydrocarbon feed were used. The results for threedifferent isomers are listed:

The cerium-containing catalyst of Example 1 was used in the productionof butadiene from a feed containing mixed isomers of n-butene. Asbefore, about five volumes of air were mixed with one volume of themixed monoolefin feed, and about nine volumes of steam were added as adiluent. The following results were obtained:

Run H I J K Feed mixture:

Percent 1-butene 1. 1 51. 8 35. 35. 7 Percent t-2-butene 51. 8 26. 2 35.0 34. Percent e-2-butene 43. 9 20. 7 28. 1 27. 8 Percent n-butane 3.0 1. 2 1. 7 Temp, C 510 505 512 510 GHSV 156 153 146 149 Percentconversion. 78. 0 80. 0 85. 0 84. 0 Percent selectivity 76. 3 80. 9 78.9 82. 2 Percent butadiene yield 59. 7 65. 0 67. 0 69. 0 Percent 002--12. 1 10. 2 12. 7 9. 5 Percent 00. 5. 5 4. 5 4. 2 4. 6 Percent coke-. 0.17 0. l8 0. 5 0. 06

We claim:

1. A process for conversion of a mono-olefinic compound having from 4 to7 carbon atoms to the corresponding conjugated diolefin by contacting amixture of said mono-olefinic compound and oxygen with a catalystcomprised of a mixture of oxides of bismuth and molybdenum having abismuth to molybdenum atomic ratio of at least 0.1 and minor amounts ofcerium oxide as a promoter at a temperature of from 350 C. to 650 C.

2. The process of claim 1 in which the molar ratio of oxygen to saidmono-olefinic compound is from about 0.311 to about 2:1.

3. The process of claim 1 in which said mono-olefinic compound is anormal butene.

4. The process of claim 1 in which said mono-olefinic compound is apentene.

S. The process of claim 1 in which steam is added as a diluent to themixture of said mono-olefinic compound and oxygen.

6. The process of claim 1 in which said mono-olefinic compound iscomprised of mixed n-butenes.

7. The process of claim 2 in which said mono-olefinic compound isl-butene, the oxygen is in the form of atmospheric air, the atomic ratioof molybdenum to bismuth to cerium is to 71.5 to 2.87, and steam isadded as a diluent to the mixture of said mono-olefinic compound andoxygen.

References Cited UNITED STATES PATENTS 2,991,320 7/1961 Hearne et 211.3,251,900 5/ 1966 Callahan et a1. 3,320,330 5/1967 Callahan et al.

PAUL M. COUGHLAN, Primary Examiner U.S. Cl. X.R. 252462; 260666

